Tank IDENTITY

[Shurrikhan]

if anything, I would just want to keep arm's length for all melee, and swiftcast and lucid dreaming for casters.

Even those three are a waste.

• Arm's Length and Surecast exists only to replace all two-minute knockback mechanics with a button instead of pre-positioning (which is both generally more interesting and costs... no buttons).
• Lucid Dreaming may as well just be baseline increased MP generation or reduced MP costs.
• Swiftcast on Casters has no application outside of early Flare (Ruby Rite has a longer recast time, too, not just cast time, so it's wasted there), already likely overpowered caster rezzes.
• Provoke could easily give a further bump of temporary Enmity and thereby remove any need whatsoever for Shirk (not that there's a need even now).
• Bloodbath and Second Wind could be more interestingly handled by job-specific sustain tools instead of scavenging a Marauder and Pugilist skill each.
• By all means, bring back stuns attached to (especially if bankable) damage oGCDs; this game's garbage diminishing returns system needs replacement anyways, so it's time to stop simply throwing a rug over the real problem.
• Not every Physical Ranged needs a full suite of CC forms in all the same ways. Let En Avant through enemies and Venomous/Caustic Bite, for instance, apply the Heavy, and let other skills apply other CC forms, etc.

Just trim all Role Actions entirely, give tanks their own version each of Provoke, give healers their own unique rez spells and/or Swiftcast-like abilities better fit to their kits, and give non-casters a further sustain tool (or further potency to their existing ones) that'd synergize or at least fit thematically with their kits.

You forgot the part about Arm's Length being also a mitigation tool in dungeons.

Not forgetting it; it's just a capacity that could all too easily be offloaded to anywhere else and thereby avoid that button bloat / added point of homogeneity.